1. Field of the Invention
The present invention relates to a process for preparing a cationic electrodeposition-coating resin.
2. Description of the Prior Arts
An electrodeposition process by using a water soluble resin or a water dispersible resin has been developed for a base coating (the first prime coat) on a car. Novel resins have been further developed for the purpose of improvement of anticorrosive property. However, it has not attained to provide a satisfactory resin.
In the conventional anionic electrodeposition process, a metal substrate is connected to an anode whereby the metal substrate and the pretreated layer thereof are dissolved. The anticorrosive property thereof has not been satisfactory.
It has been proposed to provide a cationic electrodeposition-coating resin and process which do not cause dissolution of a metal substrate. However, resins produced hitherto are hardly, practically applicable in view of an anticorrosive property, a mechanical property and a stability for storing as a coating composition.
The inventors have studied on electrodeposition processes which have not the above-mentioned disadvantages. It has been found to overcome these disadvantages by a cationic electrodeposition by using a paint comprising thermosettable cationic aqueous urethane resin. These inventions have been disclosed in U.S. Pat. No. 3,823,118, and Japanese Patent Publication Nos. 47519/1977, 47520/1977, 6663/1978, 2894/1978 and 2895/1978.
The inventors have further studied to improve the characteristics of the cationic electrodeposition process.